Continuous flow synthesis of metal nanowires: protocols, engineering aspects of scale-up and applications

This review comprehensively covers the translation from batch to continuous flow synthesis of metal nanowires (i.e., silver, copper, gold, and platinum nanowires) and their diverse applications across various sectors. Metal nanowires have attracted significant attention owing to their versatility and feasibility for large-scale synthesis. The efficacy of flow chemistry in nanomaterial synthesis has been extensively demonstrated over the past few decades. Continuous flow synthesis offers scalability, high throughput screening, and robust and reproducible synthesis procedures, making it a promising technology. Silver nanowires, widely used in flexible electronics, transparent conductive films, and sensors, have benefited from advancements in continuous flow synthesis aimed at achieving high aspect ratios and uniform diameters, though challenges in preventing agglomeration during large-scale production remain. Copper nanowires, considered as a cost-effective alternative to silver nanowires for conductive materials, have benefited from continuous flow synthesis methods that minimize oxidation and enhance stability, yet scaling up these processes requires precise control of reducing environments and copper ion concentration. A critical evaluation of various metal nanowire ink formulations is conducted, aiming to identify formulations that exhibit superior properties with lower metal solid content. This study delves into the intricacies of continuous flow synthesis methods for metal nanowires, emphasizing the exploration of engineering considerations essential for the design of continuous flow reactors. Furthermore, challenges associated with large-scale synthesis are addressed, highlighting the process-related issues.

Preparation of silver nanowires with controlled parameters for conductive transparent electrodes

Silver nanowires (AgNWs) have excellent flexibility, unique optical transmittance and high conductivity. The polyol process is appropriate for preparing AgNWs due to its simplicity, effectiveness, low cost, and high yield. This work aims to investigate the effect of preparation parameters of the polyol process on the silver nanowires properties. The parameters include the controlling agent, molecular weight of the polyvinylpyrrolidone (PVP), the temperature, and the reducing agent. The amount of silver nanoparticles formed during preparation was used to determine the optimum preparation conditions. The transmission electron microscope (TEM) images showed minimal amount of Ag nanoparticles when using mixed molecular weight of PVP-40K, and PVP-1.3M at 150 °C with the assistance of copper chloride as a controlling agent. The prepared AgNWs had an average length of 3.7 µm and aspect ratio of 15.3. The fabricated electrodes were characterized using a scanning electron microscope (SEM) and four probe resistivity measurements. The electrical measurement of the AgNWs electrodes indicated that the surfactant thickness is a critical parameter in having low sheet resistance electrodes. Also, the optical transmission was affected by the amount of nanoparticles. The prepared electrode with high concentration of AgNWs and a minimal amount of nanoparticles exhibited 80% optical transmission.

Preparation of anisotropic AgNWs/PVA/Ag2S nanocomposites via a vapor-phase sulfidation process

This study used a modified polyol technique to synthesize silver nanowires (AgNWs), which were subsequently mixed with polyvinyl alcohol (PVA) polymer and air-dried under ambient conditions. As a result, AgNWs/PVA nanocomposites with a concentration of 2% were prepared by a casting process. After that, the upper surface of the produced samples was treated with H2S gas, as a result of which asymmetric structures were formed depending on the gas concentration, exposure time and penetration into the layers. The structural, morphological, and optical properties of these asymmetric structures were analyzed. Changes in the sample structure were studied using X-ray diffraction (XRD), their optical properties were studied using ultraviolet-visible (UV-Vis), Raman spectroscopy, and their morphology using Transmission electron microscopy (TEM). A simple technique involving H2S gas was used for the sulfidation process of the samples, marking the first exposure of AgNW/PVA nanocomposites to such treatment. Examination of the structural and optical properties of the surfaces revealed clear differences in their physical properties after sulfidation. These obtained results were also supported by TEM images. Finally, the successful production of AgNWs/PVA/Ag2S anisotropic structure was achieved by this method.

Soft Electronics for Health Monitoring Assisted by Machine Learning

Due to the development of the novel materials, the past two decades have witnessed the rapid advances of soft electronics. The soft electronics have huge potential in the physical sign monitoring and health care. One of the important advantages of soft electronics is forming good interface with skin, which can increase the user scale and improve the signal quality. Therefore, it is easy to build the specific dataset, which is important to improve the performance of machine learning algorithm. At the same time, with the assistance of machine learning algorithm, the soft electronics have become more and more intelligent to realize real-time analysis and diagnosis. The soft electronics and machining learning algorithms complement each other very well. It is indubitable that the soft electronics will bring us to a healthier and more intelligent world in the near future. Therefore, in this review, we will give a careful introduction about the new soft material, physiological signal detected by soft devices, and the soft devices assisted by machine learning algorithm. Some soft materials will be discussed such as two-dimensional material, carbon nanotube, nanowire, nanomesh, and hydrogel. Then, soft sensors will be discussed according to the physiological signal types (pulse, respiration, human motion, intraocular pressure, phonation, etc.). After that, the soft electronics assisted by various algorithms will be reviewed, including some classical algorithms and powerful neural network algorithms. Especially, the soft device assisted by neural network will be introduced carefully. Finally, the outlook, challenge, and conclusion of soft system powered by machine learning algorithm will be discussed.

Doping of Transparent Electrode Based on Oriented Networks of Nickel in Poly(3,4-Ethylenedioxythiophene) Polystyrene Sulfonate Matrix with P-Toluenesulfonic Acid

This work aimed to obtain an optically transparent electrode based on the oriented nanonetworks of nickel in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate matrix. Optically transparent electrodes are used in many modern devices. Therefore, the search for new inexpensive and environmentally friendly materials for them remains an urgent task. We have previously developed a material for optically transparent electrodes based on oriented platinum nanonetworks. This technique was upgraded to obtain a cheaper option from oriented nickel networks. The study was carried out to find the optimal electrical conductivity and optical transparency values of the developed coating, and the dependence of these values on the amount of nickel used was investigated. The figure of merit (FoM) was used as a criterion for the quality of the material in terms of finding the optimal characteristics. It was shown that doping PEDOT: PSS with p-toluenesulfonic acid in the design of an optically transparent electroconductive composite coating based on oriented nickel networks in a polymer matrix is expedient. It was found that the addition of p-toluenesulfonic acid to an aqueous dispersion of PEDOT: PSS with a concentration of 0.5% led to an eight-fold decrease in the surface resistance of the resulting coating.

Continuous Patterning of Silver Nanowire-Polyvinylpyrrolidone Composite Transparent Conductive Film by a Roll-to-Roll Selective Calendering Process

The roll-to-roll (R2R) continuous patterning of silver nanowire-polyvinylpyrrolidone (Ag NW-PVP) composite transparent conductive film (cTCF) is demonstrated in this work by means of slot-die coating followed by selective calendering. The Ag NWs were synthesized by the polyol method, and adequately washed to leave an appropriate amount of PVP to act as a capping agent and dispersant. The as-coated Ag NW-PVP composite film had low electronic conductivity due to the lack of percolation path, which was greatly improved by the calendering process. Moreover, the dispersion of Ag NWs was analyzed with addition of PVP in terms of density and molecular weight. The excellent dispersion led to uniform distribution of Ag NWs in a cTCF. The continuous patterning was conducted using an embossed pattern roll to perform selective calendering. To evaluate the capability of the calendering process, various line widths and spacing patterns were investigated. The minimum pattern dimensions achievable were determined to be a line width of 0.1 mm and a line spacing of 1 mm. Finally, continuous patterning using selective calendering was applied to the fabrication of a flexible heater and a resistive touch sensing panel as flexible electronic devices to demonstrate its versatility.

Preparation of Low Volatile Organic Compounds Silver Paste Containing Ternary Conductive Fillers and Optimization of Their Performances

Conductive silver paste is a key material in the fields of printed circuits and printed electronic devices. However, the preparation of conductive silver paste with low-cost and volatile organic compounds (VOCs) is still a challenge. In this work, conductive silver pastes with excellent comprehensive performances were developed by using water-borne polyurethane (WPU) as the bonding phase and using the ternary mixture of Ag microflakes (Ag MFs), Ag nanowires (Ag NWs), and Ag nanoparticles (Ag NPs) as the conductive phase. WPU endowed conductive silver pastes with the adhesion along with releasing a few VOCs during the curing. Results showed that a small amount of Ag NPs or Ag NWs dramatically enhanced the electrical conductivity of silver paste paint film filled only with Ag MFs. The electrical resistivity for optimal ternary mixture conductive silver paste was 0.2 × 10-3 Ω∙cm, and the conductive phase was composed of 20.0 wt% Ag MFs, 7.5 wt% Ag NWs, and 2.5 wt% Ag NPs. Meanwhile, the adhesive strength and hardness of silver paste paint film were effectively improved by increasing the curing temperature. The optimal overall performance of the conductive silver pastes was achieved at the curing temperature of 160 °C. Therefore, this work can provide a new route for preparing conductive silver pastes with high performances.

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

Optical Properties of Colloidal Silver Nanowires

Silver nanowires are used in many applications, ranging from transparent conductive layers to Raman substrates and sensors. Their performance often relies on their unique optical properties that emerge from localized surface plasmon resonances in the ultraviolet. To tailor the nanowire geometry for a specific application, a correct understanding of the relationship between the wire's structure and its optical properties is therefore necessary. However, while the colloidal synthesis of silver nanowires typically leads to structures with pentagonally twinned geometries, their optical properties are often modeled assuming a cylindrical cross-section. Here we highlight the strengths and limitations of such an approximation by numerically calculating the optical and electrical response of pentagonally twinned silver nanowires and nanowire networks. We find that our accurate modeling is crucial to deduce structural information from experimentally measured extinction spectra of colloidally synthesized nanowire suspensions and to predict the performance of nanowire-based near-field sensors. On the contrary, the cylindrical approximation is fully capable of capturing the optical and electrical performance of nanowire networks used as transparent electrodes. Our results can help assess the quality of nanowire syntheses and guide in the design of optimized silver nanowire-based devices.

ZnS Quantum Dots Decorated on One-Dimensional Scaffold of MWCNT/PANI Conducting Nanocomposite as an Anode for Enzymatic Biofuel Cell

This study aims to design a new nanocomposite as a supporting material for wiring the enzyme to develop a bioanode in the enzymatic biofuel cell (EBFC). In this work, polyaniline-based nanocomposite was synthesized by in situ polymerization of aniline monomer. The zeta potential study of the nanofillers was carried out, which reveals the interaction between the nanofillers. The synthesized nanocomposite (MWCNT/ZnS/AgNWs/PANI) was characterized by analytical techniques, such as Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction spectroscopy (XRD). Furthermore, the surface morphology and the in-depth information of the synthesized nanocomposite were displayed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. In addition, the as-synthesized nanocomposite and the designed bioanode underwent the electrochemical assessment using different electrochemical techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) for evaluating the electrochemical behavior of the fabricated anodes. The electrochemically regulated bioanode (MWCNT/ZnS/AgNWs/PANI/Frt/GOx) obtained an open-circuit voltage of 0.55 V and produced a maximal current density of 7.6 mA cm⁻² at a glucose concentration of 50 mM prepared in phosphate buffer solution (PBS) (pH 7.0) as a supporting electrolyte at a scan rate of 100 mV s⁻¹.

Metal Nanoparticles and Carbon-Based Nanomaterials for Improved Performances of Electrochemical (Bio)Sensors with Biomedical Applications

Monitoring human health for early detection of disease conditions or health disorders is of major clinical importance for maintaining a healthy life. Sensors are small devices employed for qualitative and quantitative determination of various analytes by monitoring their properties using a certain transduction method. A "real-time" biosensor includes a biological recognition receptor (such as an antibody, enzyme, nucleic acid or whole cell) and a transducer to convert the biological binding event to a detectable signal, which is read out indicating both the presence and concentration of the analyte molecule. A wide range of specific analytes with biomedical significance at ultralow concentration can be sensitively detected. In nano(bio)sensors, nanoparticles (NPs) are incorporated into the (bio)sensor design by attachment to the suitably modified platforms. For this purpose, metal nanoparticles have many advantageous properties making them useful in the transducer component of the (bio)sensors. Gold, silver and platinum NPs have been the most popular ones, each form of these metallic NPs exhibiting special surface and interface features, which significantly improve the biocompatibility and transduction of the (bio)sensor compared to the same process in the absence of these NPs. This comprehensive review is focused on the main types of NPs used for electrochemical (bio)sensors design, especially screen-printed electrodes, with their specific medical application due to their improved analytical performances and miniaturized form. Other advantages such as supporting real-time decision and rapid manipulation are pointed out. A special attention is paid to carbon-based nanomaterials (especially carbon nanotubes and graphene), used by themselves or decorated with metal nanoparticles, with excellent features such as high surface area, excellent conductivity, effective catalytic properties and biocompatibility, which confer to these hybrid nanocomposites a wide biomedical applicability.

High-yield synthesis of silver nanowires for transparent conducting PET films

Silver nanowires (AgNWs) with ultrahigh purity and high yield were successfully synthesized by employing a modified facile polyol method using PVP as a capping and stabilizing agent. The reaction was carried out at a moderate temperature of 160 °C under mild stirring for about 3 h. The prepared AgNWs exhibited parallel alignment on a large scale and were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and PL spectroscopy. The luminescent AgNWs exhibited red emission, which was accredited to deep holes. The SEM results confirmed the formation of AgNWs of 3.3 to 4.7 µm in length with an average diameter of about 86 nm, that is, the aspect ratio values of the AgNWs exceeded 45. An ink consisting of hydroxyethyl cellulose (HEC) and AgNWs was transferred to polyethylene terephthalate (PET) films by simple mechanical pressing. The PET films retained transparency and flexibility after the ink coating. The maximum transmittance value of as-prepared PET films in the visible region was estimated to be about 92.5% with a sheet resistance value of ca. 20 Ω/sq. This makes the films a potential substitute to commonly used expensive indium tin oxide (ITO) in the field of flexible optoelectronics.

Recent Developments in Flexible Transparent Electrode

With the rapid development of flexible electronic devices (especially flexible LCD/OLED), flexible transparent electrodes (FTEs) with high light transmittance, high electrical conductivity, and excellent stretchability have attracted extensive attention from researchers and businesses. FTEs serve as an important part of display devices (touch screen and display), energy storage devices (solar cells and super capacitors), and wearable medical devices (electronic skin). In this paper, we review the recent progress in the field of FTEs, with special emphasis on metal materials, carbon-based materials, conductive polymers (CPs), and composite materials, which are good alternatives to the traditional commercial transparent electrode (i.e., indium tin oxide, ITO). With respect to production methods, this article provides a detailed discussion on the performance differences and practical applications of different materials. Furthermore, major challenges and future developments of FTEs are also discussed.

Silver Nanowire Synthesis and Strategies for Fabricating Transparent Conducting Electrodes

One-dimensional metal nanowires, with novel functionalities like electrical conductivity, optical transparency and high mechanical stiffness, have attracted widespread interest for use in applications such as transparent electrodes in optoelectronic devices and active components in nanoelectronics and nanophotonics. In particular, silver nanowires (AgNWs) have been widely researched owing to the superlative thermal and electrical conductivity of bulk silver. Herein, we present a detailed review of the synthesis of AgNWs and their utilization in fabricating improved transparent conducting electrodes (TCE). We discuss a range of AgNW synthesis protocols, including template assisted and wet chemical techniques, and their ability to control the morphology of the synthesized nanowires. Furthermore, the use of scalable and cost-effective solution deposition methods to fabricate AgNW based TCE, along with the numerous treatments used for enhancing their optoelectronic properties, are also discussed.

A one-step synthesis of ultra-long silver nanowires with ultra-high aspect ratio above 2000 and its application in flexible transparent conductive electrodes

Silver nanowires (AgNWs), appear as an extremely promising candidate for the next generation of flexible transparent conductive electrodes (FTCEs). However, the performance of AgNWs-FTCEs was severely limited by the aspect ratio of AgNWs, while it was still a big challenge to fabricate AgNWs with high aspect ratio nowadays. To improve the aspect ratio of AgNWs, bromide ion (Br^-), cupric ion (Cu²⁺) and polyvinylpyrrolidone (PVP, Mw ≈ 1300 000) which are beneficial for the synthesis of high aspect ratio AgNWs, were introduced in this article. The high quality and uniform AgNWs with the average diameter of 77.6 nm and the aspect ratio above 2000 were fabricated via a one-step solvothermal method. The effects of reaction time, molar ratio of AgNO₃ to PVP and the concentration of CuBr₂ on the aspect ratio of AgNWs were discussed. The mechanism of the synthesis of high aspect ratio AgNWs was explored. After that, the prepared AgNWs were spin-coated on the surface of PET film, the FTCEs based on the ultra-high aspect ratio AgNWs without any post-treatments exhibits relatively high transmittance, low haze and low sheet resistance, and the AgNWs have little effect on the optical performance of pristine PET film. The outstanding performance of the prepared FTCEs indicated that the ultra-high aspect ratio AgNWs are ideal materials in the application of FTCEs, and the method of fabricating AgNWs could provide a direction to the high aspect ratio AgNWs.

Highly Transparent Conducting Electrodes Based on a Grid Structure of Silver Nanowires

Transparent conducting electrodes (TCEs) formed with silver nanowires (AgNWs) have attracted attention as substitutes for indium tin oxide (ITO). However, the randomly deposited AgNW film performs poorly in terms of the transmittance and sheet resistance to serve as a substitute of ITO. To improve the performance of the AgNW film, we fabricated a grid-patterned AgNW by modifying the surface energy of the substrate. The hydrophobized surface was selectively etched by UV light through a quartz chrome mask, and a suspension of AgNWs in isopropyl alcohol/ethylene glycol mixture was coated on the substrate by a meniscus dragging deposition process. The grid-patterned AgNW film has a lower percolation threshold and a 13% higher figure-of-merit value compared to the randomly deposited AgNW film. The transparent thin films with a grid structure of AgNWs exhibit the high electrical conductivity with a sheet resistance of 33 Ohm/sq at a transmittance of 92.7% (λ = 550 nm).

Transformation of industrial wastewater into copper-nickel nanowire composites: straightforward recycling of heavy metals to obtain products of high added value

Large amounts of industrial metal containing process and waste solutions are a growing issue. In this work, we demonstrated that they could be transformed into materials of high added values such as copper-nickel nanowires (CuNi NWs) by simple chemical reduction. A thorough investigation of the parameter space was conducted. The microstructure of the obtained material was found tunable depending on the employed concentration of precursor, reducing agent, capping agent, pH, temperature, and reaction time. Moreover, the obtained product had a strong magnetic character, which enabled us to separate it from the reaction medium with ease. The results open new perspectives for materials science by proposing a new type of nanostructure: composite NWs of very promising properties, with metallic elements originating directly from industrial process solution.

Simple and Fast High-Yield Synthesis of Silver Nanowires

Silver nanowires (AgNWs) combine high electrical conductivity with low light extinction in the visible and are used in a wide range of applications, from transparent electrodes, to temperature and pressure sensors. The most common strategy for the production of AgNWs is the polyol synthesis, which always leads to the formation of silver nanoparticles as byproducts. These nanoparticles degrade the performance of AgNWs' based devices and have to be eliminated by several purification steps. Here, we report a simple and fast synthesis of AgNWs with minimal formation of byproducts, as confirmed by the spectral purity of the final solution. Our synthetic strategy relies on the use of freshly prepared AgCl and on the minimization of gas evolution inside the reaction vessel. The observed synthetic improvements can be of general validity for the polyol synthesis of metallic nanostructures of different shapes and compositions.

Highly efficient and stable transparent electromagnetic interference shielding films based on silver nanowires

Transparent electromagnetic interference (EMI) shielding materials with high optical transmittance and outstanding shielding effectiveness (SE) for optoelectronic devices in visual windows are urgently needed. Herein, we demonstrate the preparation of a transparent EMI shielding film based on silver nanowires (Ag NWs) via a facile Mayer-rod coating method. The electrical conductivity and transmittance of Ag NW-based films can be greatly improved through treatment with NaBH₄ and the lamination of poly(diallyldimethyl-ammonium chloride). The coverage of the polymer decreases the surface roughness, with no damage on the uniform mesh of the Ag NWs. The Ag NW/PDDA composite films present a sheet resistance of 22 Ω sq^-1 at a transmittance of 95.5%, better than that of commercial indium tin oxide (ITO). The excellent optoelectrical performance of the Ag NW/PDDA composite film is further ascertained by fitting the transmittance with the resistance, with a figure of merit of 443. The Ag NW/PDDA composite films in this study exhibit greatly improved stability during 25 °C/65% RH aging for 35 days with the assistance of the coverage layer. Moreover, the EMI SE of the Ag NW/PDDA composite films is 28 dB on average at a transmittance of 91.3%, and continuously increases to 31.3 dB while the optical transmittance is still maintained at 86.8%, which is superior to those of most reported transparent EMI shielding materials. Taken together, the excellent optical transmittance and EMI shielding performance of the Ag NW/PDDA composite film make it an outstanding transparent EMI shielding material in optoelectronic devices, such as aerospace equipment, medical devices, communication facilities, and electronic displays.

Optimization of rGO-PEI/Naph-SH/AgNWs/Frt/GOx nanocomposite anode for biofuel cell applications

The present study reports a new nanocomposite design using surface modified silver nanowires decorated on the surface of polyethyleneimine (PEI), a cationic polymer acting as glue for anchoring nanowires and reduced graphene oxide (rGO). The synthesized nanocomposite was employed as a promising electrode material for immobilization of biomolecules and effective transportation of electron, in enzymatic biofuel cell (EBFCs) application. The synthesized nanocomposite was confirmed by analytical techniques, for instance, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The electrochemical behaviour of the nanobioelectrocatalysts rGO-PEI/Frt/GOx, rGO-PEI/AgNWs/Frt/GOx, and rGO-PEI/Naph-SH/AgNWs/Frt/GOx was determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The maximum current density obtained by the modified bioanode was found to be 19.9 mA cm⁻² at the limiting glucose concentration of 50 mM in PBS (pH 7.0) as supporting electrolyte at a scan rate of 100 mVs⁻¹.

A one-step-assembled three-dimensional network of silver/polyvinylpyrrolidone (PVP) nanowires and its application in energy storage

Creating ultralight monolithic metal foams remains an outstanding challenge despite their important applications, e.g., in electronics, sensors and energy storage. Herein, a facile methodology is developed for one-step fabrication of silver/polyvinylpyrrolidone (PVP) nanowire (AgPNW) hydrogel and high-quality robust ultralight AgPNW aerogel (AgPNWA) on a large scale. The hydrogel is directly formed by in situ assembling hydrothermally-synthesized AgPNWs. The resultant ultralight AgPNWA exhibits very high electrical conductivity. The application of this one-step fabricated AgPNWA to enhance phase change materials (PCMs) for high-efficiency thermal energy storage is investigated. The AgPNWA-paraffin composite (APC) shows ∼350% thermal-efficiency enhancement, ∼463% mechanical hardening, and strong reliability against thermal cycling due to the potentially strong AgPNW-paraffin interfacial interaction. It is also observed that the thickness of the APC shrinks significantly but there is no change in its diameter during thermal cycles. Analytical models of liquid capillary filling of deformable fiber-based 3D networks are derived for the first time and are applied to analyze the thermal-cycling-induced-shape-stabilization behavior of the APC and the vaporization-induced collapse behavior of the AgPNW network. This work provides important insights into designing a facile 3D assembly of nanomaterials, and thermal energy storage materials with high performance and reliability.

The synthesis of silver nanowires with tunable diameters using halide ions for flexible transparent conductive films

The diameter of Ag nanowires could be tuned in the range of 19 to 35 nm with the cooperation of Cl⁻ and Br⁻ ions.

High Aspect Ratio and Post-Processing Free Silver Nanowires as Top Electrodes for Inverted-Structured Photodiodes

Silver nanowires (Ag NWs) as transparent conducting electrodes are widely used in many applications such as organic light-emitting diodes (OLEDs), polymer light-emitting diodes, touch screens, solar cells, and transparent heaters. In this work, using a large-scale synthesis, the synthesized Ag NWs had a high aspect ratio of 2820. The Ag NWs could be applied as a top transparent electrode in a device by simple drop-casting without any post-processing steps. The fabricated device comprised 4,4'-bis(carbazol-9-yl)biphenyl/MoO3 organic/inorganic layers which are parts of the inverted structure OLEDs or solar cells. The photodiode characteristics at the UV range were observed in the device. The ability of Ag NWs to replace opaque metals as top electrodes in a device has been demonstrated.

Movement-reactor oven and wire mesh filter for large-scale solvothermal preparation and purification of silver nanowires with high uniformity in length and diameter for the fabrication of low and high haze transparent conductive films

Conventional polyol synthesis has been widely used for the preparation of metal nanowires with different aspect ratios. However, its main drawback is that it is difficult to control the reaction parameters for the shape-controlled synthesis of metal nanowires. Although with the solvothermal method the shape control and growth rate improve, but on a large scale, there are still some challenges such as high reactor weight, long processing time and non-heat uniformity in different positions of the oven. In addition, the purification of nanowires on a large scale is another challenge in this area. Herein, we report the use of a movement reactor oven with the ability to rotate the reactors, and high heat conductive, light-weight reactors for the large-scale preparation of silver nanowires with highly uniform lengths and diameters. The uniformity of the length and diameter of the nanowires using the movement reactor oven in comparison with that using the fixed-reactor oven significantly improved. Furthermore, the amount of silver nanowires increased by 20 times using the new reactor in comparison with the standard Teflon-lined stainless steel reactor for the same reaction time. Reactor rotation, as a new parameter to adjust the final product, was introduced. The synthesized nanowires with and without rotation showed the same morphology and electrical conductivity. For the purification step, first, a new angular filtration method using a wire mesh filter was applied to separate the solvents and ionic impurities, and then by using the same filter based on tangential flow, the nanowires were separated from nanoparticles. Finally, uniform and coffee ring-free transparent conductive films (TCFs) with different haze values were fabricated by coating the formulated silver nanowire ink containing a mixture of green solvents. The fabricated films can be potentially used in a wide range of applications.

Controllable assembly of a hierarchical multiscale architecture based on silver nanoparticle grids/nanowires for flexible organic solar cells

In this work, an effective and facile strategy was developed to assemble a flexible hierarchical multiscale architecture by incorporating microscale silver nanoparticles (AgNPs) grids into random silver nanowires (AgNWs) networks combined with a room-temperature chemical sintering mechanism. The microscale AgNPs grids was fabricated by assemble AgNPs into a series of twin lines directly on a hydrophilic PET substrate based on coffee-ring effect with ink-jet printing technique. By regulating the assembly architecture, a flexible hierarchical multiscale conductor based on AgNPs grids/AgNWs was successfully fabricated and demonstrated a high transmittance of 87.5%, low sheet resistance of 16.5 Ω/sq and excellent mechanical flexibility. The hierarchical multiscale architecture was fairly favorable to efficiently collect free charges among the gaps in the AgNWs network, as well as to enhance the stability of conductivity by creating continuous conduction pathways. As an anode electrode in a flexible organic solar cell, the hierarchical multiscale AgNPs grids/AgNWs conductor demonstrated a more power photoelectric conversion efficiency, which was even superior to the corresponding properties of the ITO network at a similar transmittance. This simple, low-cost and nonlithographic solution-based approach would further enhance current fabrication approaches to create patterned microstructures, and have great potential to fabricate multifarious functional patterns in flexible electronic devices.

Controllable synthesis of AgNWs@PDA@AgNPs core-shell nanocobs based on a mussel-inspired polydopamine for highly sensitive SERS detection

In this work, a series of AgNWs@PDA@AgNPs core-shell nanocobs based on a mussel-inspired polydopamine (PDA) were controllably synthesized and achieve highly sensitive SERS detection. Owing to the existence of abundant catechol and amine functional groups, PDA molecules could assemble a functional layer on the surface of silver nanowires (AgNWs) and exhibit exceptional adhesion performance. More importantly, silver nanoparticles (AgNPs) with controlled coverage and size were achieved on the surface of the PDA layer by in situ reduction of silver ions into AgNPs with catechol functional groups, forming AgNWs@PDA@AgNPs core-shell nanocobs. By regulating synergistical effect between the AgNWs and AgNPs, the AgNWs@PDA@AgNPs core-shell nanocobs demonstrated a highly sensitive and stable SERS response to Rhodamine 6G (R6G) molecules, and a low limit of detection down to 10-12 M. Furthermore, the AgNWs@PDA@AgNPs core-shell nanocobs showed an excellent reproducibility and superior stability as a SERS substrate to achieve trace detection. This strategy would have great potential to fabricate multifarious SERS-active substrates that make it possible to detect single molecules and singles cell in chemical and biological fields.

Advancements in Copper Nanowires: Synthesis, Purification, Assemblies, Surface Modification, and Applications

Copper nanowires (CuNWs) are attracting a myriad of attention due to their preponderant electric conductivity, optoelectronic and mechanical properties, high electrocatalytic efficiency, and large abundance. Recently, great endeavors are undertaken to develop controllable and facile approaches to synthesize CuNWs with high dispersibility, oxidation resistance, and zero defects for future large-scale nano-enabled materials. Herein, this work provides a comprehensive review of current remarkable advancements in CuNWs. The Review starts with a thorough overview of recently developed synthetic strategies and growth mechanisms to achieve single-crystalline CuNWs and fivefold twinned CuNWs by the reduction of Cu(I) and Cu(II) ions, respectively. Following is a discussion of CuNW purification and multidimensional assemblies comprising films, aerogels, and arrays. Next, several effective approaches to protect CuNWs from oxidation are highlighted. The emerging applications of CuNWs in diverse fields are then focused on, with particular emphasis on optoelectronics, energy storage/conversion, catalysis, wearable electronics, and thermal management, followed by a brief comment on the current challenges and future research directions. The central theme of the Review is to provide an intimate correlation among the synthesis, structure, properties, and applications of CuNWs.

Augmented Quantum Yield of a 2D Monolayer Photodetector by Surface Plasmon Coupling

Monolayer (1L) transition metal dichalcogenides (TMDCs) are promising materials for nanoscale optoelectronic devices because of their direct band gap and wide absorption range (ultraviolet to infrared). However, 1L-TMDCs cannot be easily utilized for practical optoelectronic device applications (e.g., photodetectors, solar cells, and light-emitting diodes) because of their extremely low optical quantum yields (QYs). In this investigation, a high-gain 1L-MoS₂ photodetector was successfully realized, based on the surface plasmon (SP) of the Ag nanowire (NW) network. Through systematic optical characterization of the hybrid structure consisting of a 1L-MoS₂ and the Ag NW network, it was determined that a strong SP and strain relaxation effect influenced a greatly enhanced optical QY. The photoluminescence (PL) emission was drastically increased by a factor of 560, and the main peak was shifted to the neutral exciton of 1L-MoS₂. Consequently, the overall photocurrent of the hybrid 1L-MoS₂ photodetector was observed to be 250 times better than that of the pristine 1L-MoS₂ photodetector. In addition, the photoresponsivity and photodetectivity of the hybrid photodetector were effectively improved by a factor of ∼1000. This study provides a new approach for realizing highly efficient optoelectronic devices based on TMDCs.

Emerging Novel Metal Electrodes for Photovoltaic Applications

Emerging novel metal electrodes not only serve as the collector of free charge carriers, but also function as light trapping designs in photovoltaics. As a potential alternative to commercial indium tin oxide, transparent electrodes composed of metal nanowire, metal mesh, and ultrathin metal film are intensively investigated and developed for achieving high optical transmittance and electrical conductivity. Moreover, light trapping designs via patterning of the back thick metal electrode into different nanostructures, which can deliver a considerable efficiency improvement of photovoltaic devices, contribute by the plasmon-enhanced light-mattering interactions. Therefore, here the recent works of metal-based transparent electrodes and patterned back electrodes in photovoltaics are reviewed, which may push the future development of this exciting field.

Facile synthesis of Ag/ZnO metal–semiconductor hierarchical photocatalyst nanostructures via the galvanic-potential-enhanced hydrothermal method

Hierarchical metal–semiconductor nanostructures composed of Ag nanowire and ZnO nanorod branches were prepared by using the galvanic-potential-enhanced hydrothermal method.

A facile synthesis of segmented silver nanowires and enhancement of the performance of polymer solar cells

Segmented AgNWs synthesized by a polyol method at a suitable reaction temperature and time were blended into PEDOT:PSS hole transporting layers to enhance the performance of polymer solar cells.

One-Pot Synthesis and Purification of Ultralong Silver Nanowires for Flexible Transparent Conductive Electrodes

Metal nanowires (NWs) have become the most promising candidates for the next generation of flexible transparent conductive electrodes (FTCEs), with high transmittance and low sheet resistance. In this work, ultralong silver NWs (Ag NWs), ∼220 μm (even larger than 400 μm) in length and ∼55 nm in diameter (aspect ratio: ∼4000), were synthesized via a one-pot polyol process using high molecular weight poly(vinylpyrrolidone) (M_w = 1 300 000) and an appropriate concentration of FeCl₃ (12.5 μM) through hydrothermal reaction. The prepared Ag NWs were purified by a filter cloth (pore size: about 30 × 50 μm²) to remove the Ag nanoparticles and short-length Ag NWs. The FTCE based on the ultralong Ag NWs without any post-treatments exhibits low sheet resistance of 155.0 Ω sq^-1 and transmittance of 97.70% at 550 nm. The outstanding performance of FTECs demonstrated that the ultralong Ag NWs are ideal materials for applications in flexible transparent optical devices.

Integrating spin-crossover nanoparticles with silver nanowires: toward magnetic and conductive bifunctional nanomaterials

Unprecedented 1D coaxial heterogeneous nanocomposites with spin-crossover and conductive properties were obtained by in situ growing classic magnetic bistable compounds on silver nanowires.